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Drain Gauge User's Manual <br />a Theory <br />3.Theory <br />How - Drain Gauge Works <br />The Drain Gauge is first installed below the root zone. <br />Water infiltrates down through the divergence control <br />tube, and then down a fiberglass wick into a collector. <br />As collected water fills the measurement reservoir, the <br />water level is monitored by a water depth sensor. When <br />the water level in the measurement reservoir reaches the <br />top of the siphon tube, the water empties and the event is <br />recorded by an attached data logger. The emptied water <br />then drains into the sampling reservoir. A sampling <br />syringe, attached to the water reservoir sampling port <br />(blue tube), can draw water samples out of the sampling <br />reservoir for chemical analysis. Excess water drains out of <br />an overflow port and into the soil while allowing a volume <br />of water to remain for sampling (see fig. 2). <br />A soil water balance takes into consideration the inputs, <br />losses and storage of water in a soil profile. An important <br />component of the water balance is the water that drains <br />from the bottom of the soil profile, often referred to as <br />"deep drainage" or "deep percolation." This is water that <br />has gone sufficiently far below the root zone that it cannot <br />be removed from the soil by transpiration or evaporation. <br />The other components of the water balance can be mea- <br />sured, but the deep drainage typically has been computed <br />as the remainder when the other components were mea - <br />14 <br />